GC‐MS Investigation of Organosilicon and Fluorocarbon Fed Plasmas

Fracassi

2011

This study deals with the investigation by means of gas chromatography‐mass spectrometry (GC‐MS) of the exhaust gas of an rf low pressure (LP) glow discharge and of an atmospheric pressure (AP) FDBD fed with hexamethyldisiloxane (HMDSO), O2, and Ar. The influence of feed composition on monomer depletion and on the qualitative–quantitative distribution of stable by‐products formed by recombination of plasma intermediates is investigated. Without O2 addition to the feed almost comparable values of HMDSO depletion are observed both at low and AP. Oxygen addition does not influence the monomer depletion at LP while it induces a slight decrease of the depletion at AP. Whatever the working pressure, O2 controls the overall chemistry of the plasma, since it influences the concentration of by‐products (e.g., silanes, silanols, linear, and cyclic methylsiloxanes). At AP evidences of the importance of methyl abstraction from HMDSO molecule have been obtained, while at LP the prevalence of Si–O bond rupture, of fragmentation, and oligomerization reactions is observed. The comparison of results from the GC‐MS investigation of the exhaust gas with FT‐IR spectra of the deposited coatings allows to enhance hypotheses on the formation of silanols in the gas phase and in the deposit.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

GC‐MS Investigation of Hexamethyldisiloxane–Oxygen Fed Cold Plasmas: Low Pressure Versus Atmospheric Pressure Operation

Fracassi

2011

“…GC–MS analyses show that C 3 F 6 depletion is 41% and that the by‐products detected in the exhaust gas are different from those reported by Ozaki et al in He‐C 3 F 6 glow DBDs,46 i.e., CF 4 , C 2 F 4 , C 2 F 6 , C 4 F 8 , and C 5 F 12 . In this work, in fact, only linear and cyclic fluorocarbons containing 6–8 carbon atoms have been identified 56. Among these, the presence of linear, branched, and cyclic hexanes (i.e., n‐perfluorohexane, perfluoro‐2‐methylpentane, perfluoro‐cyclohexane) suggests the occurrence of monomer dimerization reactions.…”

Section: Resultsmentioning

confidence: 79%

Effect of Gas Impurities on the Operation of Dielectric Barrier Discharges Fed with He, Ar, and Ar‐C₃F₆

Fracassi

2011

The influence of N 2 , O 2 , air, and water vapor feed gas impurities on the operation of an atmospheric pressure parallel plate DBD fed with helium and argon was investigated. The addition of increasing amounts of these impurities, under fixed excitation frequency and applied voltage, is responsible above certain thresholds of two distinct phenomena, namely the transition from a homogeneous to a filamentary appearance of the discharge and the contraction of the discharge volume. Among the different contaminants N 2 shows the highest threshold limit values, O 2 and H 2 O the lowest ones, while air generally exhibits an intermediate behavior. The effect of feed gas impurities was also studied on the PE-CVD of fluoropolymers from Ar-C 3 F 6 fed filamentary DBDs. Contaminants addition results in a decrease of the input power and of the deposition rate as well as in a change of the film morphology, however it does not influence significantly the chemical composition of the fluoropolymer film, the monomer depletion and the distribution of by-products in the exhaust gas. 0.00 0.05 0.10 0.15 0.20 0.0 0.5 1.0 1.5 2.0 [Additive] (%) N 2 O 2 Air H 2 O

“…Figure 8c–d shows that in HMDSO‐containing DBDs the flow rate of both the trimethylsilanol and hydroxypentamethyldisiloxane decreases with increasing the O 2 /HMDSO ratio, but it is never below the quantification limit. By comparing these trends with the FT‐IR spectra of the deposits (Figure 3) it can be observed that, at high O 2 /HMDSO feed ratios, the amount of SiOH groups in the film is high while the silanol content in the exhaust is very low; therefore, it is possible to rise the hypothesis that the formation of SiOH groups present in the coatings could mainly occur on the film surface through heterogeneous reactions, and not in the gas phase 26, 30. On the other hand, the reduction of the silanols content with oxygen addition in Figure 8c and d could be due to their more efficient inclusion in the growing film with consequent decrease of their gas phase concentration.…”

Section: Resultsmentioning

confidence: 95%

“…Recently we reported preliminary results on the GC‐MS investigation of the exhaust gas of filamentary DBDs fed by Ar in mixture with oxygen and different methyldisiloxanes 14, 26, 30. In particular we investigated in detail the PE‐CVD with Ar‐HMDSO‐O 2 mixtures by comparing the FT‐IR spectra of the deposited coatings with the GC‐MS analyses of the exhaust gas 26.…”

Section: Introductionmentioning

confidence: 99%

Insights into the Atmospheric Pressure Plasma‐Enhanced Chemical Vapor Deposition of Thin Films from Methyldisiloxane Precursors

Lovascio

et al. 2012

This work describes the plasma‐enhanced chemical vapor deposition of thin films at atmospheric pressure using dielectric barrier discharges fed with argon, oxygen and different methyldisiloxanes, i.e., hexamethyldisiloxane, pentamethyldisiloxane, and 1,1,3,3‐tetramethyldisiloxane. The influence of the methyldisiloxane chemical structure and of the oxygen/methyldisiloxane feed ratio is investigated in order to provide insights into the organosilicon plasma chemistry at atmospheric pressure. As expected the FT‐IR and XPS analyses show that the carbon content of the coatings depends on the number of methyl groups in the precursor molecule; in the case of coatings obtained with PMDSO and TMDSO carbon removal seems to be further enhanced by the presence of SiH bonds. Gaschromatography‐mass spectrometry analyses of the exhaust gas allow to assess the precursor depletion and to perform the quali‐quantitative determination of by‐products (e.g., silanes, siloxanes, silanols) formed by plasma activation. The results are exploited to rise hypotheses on the contribution of the different reaction pathways on the deposition mechanism.